Air pollution occurs when wastes dirty the air. People produce most of the wastes that cause air pollution. Such wastes can be in the form of gases or particulates (particles of solid or liquid matter). These substances result chiefly from burning fuel to power motor vehicles and to heat buildings. Industrial processes and the burning of garbage also contribute to air pollution. Natural pollutants (impurities) include dust, pollen, soil particles, and naturally occurring gases.
The rapid growth of population and industry, and the increased use of automobiles and airplanes, have made air pollution a serious problem. The air we breathe has become so filled with pollutants that it can cause health problems. Polluted air also harms plants, animals, building materials, and fabrics. In addition, it causes damage by altering Earth’s atmosphere.
The damage caused by air pollution costs billions of dollars each year. This includes money spent for health care and increased maintenance of buildings. Air pollution also causes damage to the environment that cannot be reversed.
Chief sources of air pollution
People depend on the atmosphere to dilute and remove pollutants as they are produced. But weather conditions called thermal inversions can trap the pollutants over a certain area until they build up to dangerous levels. A thermal inversion occurs when a layer of warm air settles over a layer of cool air that lies near the ground. This condition traps the impurities and prevents them from rising until rain or wind breaks up the layer of stationary warm air.
Forms of transportation,
such as automobiles, airplanes, ships, and trains, are the leading source of air pollution in most industrial nations. The major pollutants produced by these sources are carbon monoxide, carbon dioxide, hydrocarbons (compounds of carbon and hydrogen), and nitrogen oxides (compounds of nitrogen and oxygen). Nitrogen oxides can react with hydrocarbons in the presence of sunlight to produce a form of oxygen called ozone. Ozone is the chief component of photochemical smog, which is a common form of air pollution (see Smog).
Fuel combustion
for heating and cooling homes, office buildings, and factories contributes significantly to air pollution. Electric power plants that burn coal or oil also release pollutants into the atmosphere. The major pollutants from these sources are nitrogen oxides, sulfur oxides (compounds of sulfur and oxygen), particulates, and carbon dioxide.
Industrial processes
produce a wide range of pollutants. Oil refineries discharge ammonia, hydrocarbons, organic acids, and sulfur oxides. Metal smelting plants give off large amounts of sulfur oxides and particulates containing lead and other metals. Plants that make aluminum expel fluoride dust. By 1996, most industrialized countries, including the United States, had ended production of chlorofluorocarbons (CFC’s), compounds of chlorine, fluorine, and carbon. However, many older refrigerators and air conditioners produce CFC’s during normal operation.
Burning of solid wastes
often creates a very visible form of air pollution—thick, black smoke. It also produces invisible pollution in the form of toxic chemicals called dioxins. Many cities and towns enforce bans on the burning of garbage, leaves, and other refuse.
Other sources of pollution
include chemical sprays and organic chemicals used to start fires on charcoal grills. Forest fires and structural fires also contribute to air pollution. In rural areas and in developing countries, the burning of forests and grasslands to clear areas for farming is a major source of air pollution.
Natural sources
also contribute to air pollution. Volcanoes emit large amounts of sulfur oxides and particulates. Microbes in the digestive tracts of cattle and in rice fields break down plant materials and release an odorless gas called methane, a type of hydrocarbon.
Indoor air pollution
occurs when energy-efficient houses and office buildings trap pollutants inside. As a result, some pollutants found outdoors are found indoors in even higher concentrations. Some plastic products, processed wood products, paints, and adhesives can give off hydrocarbons. Many cleaning products emit poisonous gases, such as ammonia and chlorine. Soil and rocks release an odorless gas called radon into the atmosphere. The gas enters buildings through cracks in the foundation (see Radon).
Effects of air pollution
Health.
When people breathe polluted air, the impurities can irritate their air passages and their lungs. Particulates often remain in the lungs, and they can worsen such respiratory ailments as asthma and bronchitis. Radon can cause lung cancer if inhaled in large quantities. Certain chemical compounds can cause cancer and birth defects. Ozone reduces resistance to colds and pneumonia and can aggravate emphysema. Carbon monoxide interferes with the transfer of oxygen from the lungs to body tissues.
In London in 1952, about 4,000 people died of respiratory diseases during a “killer smog.” More than 600 people died as a result of thermal inversions that occurred in New York City in 1953 and 1963. Today, such extreme events are rare because of government emission standards, which limit the amounts of pollutants factories and other sources may release. However, air pollution still contributes to a large number of deaths each year.
Agriculture.
Air pollutants can stunt the growth of crops, harm livestock, and destroy crops. Such damage can prove costly to farmers. Forests also have been damaged by air pollution.
Atmosphere.
Some pollutants are not poisonous but can cause damage by altering Earth’s atmosphere. For example, the amount of carbon dioxide in the atmosphere has been increasing since the early to mid-1800’s, chiefly as a result of the burning of coal, oil, and other carbon-containing fuels. Carbon dioxide allows sunlight to reach Earth and warm its surface, but it prevents some surface heat from escaping out of the atmosphere. This greenhouse effect can produce significant climatic changes, which will result in great environmental challenges. See Greenhouse effect.
CFC’s break down the layer of ozone in Earth’s upper atmosphere. This layer protects plants and animals from harmful ultraviolet rays (see Ozone).
Other effects.
Most materials deteriorate faster when exposed to the pollutants present in the air. Concrete and stone are dissolved by air pollutants. Metals corrode faster than usual. Plastics, rubber, and fabrics are also damaged by air pollutants.
Air pollution is closely related to other forms of pollution. Sulfur dioxide and nitrogen oxides can react with water droplets in the air to produce acid rain. Acid rain pollutes lakes and streams and, in high concentrations, can harm soil fertility (see Acid rain).
Control of air pollution
In the United States,
all levels of government—federal, state, and local—have passed laws designed to control pollution. Congress passed the Air Quality Act in 1967. Under this act, the federal government sets goals called air quality standards for achieving cleaner air. The states must enforce air pollution controls to meet the goals. When states fail to enforce the regulations, the federal government can act against polluters by imposing fines.
The Clear Air Act of 1970, and its amendments, have set strict standards for air quality and emissions. It has required fuel producers to develop cleaner-burning fuels. It also requires automobile manufacturers to equip new vehicles with pollution-control devices called catalytic converters. In addition, the smokestacks of many electric power plants, incinerators, and factories must have scrubbers installed to remove pollutants before they can reach the air. New standards will remove most sulfur from fuels and reduce emissions of particulates. However, industry groups have repeatedly opposed stricter standards.
States may set stricter air standards than the federal government requires. Since 1970, California has set the strictest standards for motor-vehicle emissions. Several states require that a certain percentage of vehicles sold annually must be nonpolluting.
Efforts to control air pollution in the United States have been generally successful. Between 1970 and 1997, federal regulation resulted in a 98-percent reduction in lead emissions. During this same period, pollution by dust particles decreased by 75 percent. Pollution by sulfur dioxide decreased 35 percent. Both carbon monoxide and ozone emissions were reduced by more than 30 percent. Efforts to reduce nitrogen oxide pollution have met with the least success. Nitrogen oxide emissions decreased by only about 10 percent between 1970 and 1997. They increased for a number of years during this period before finally decreasing.
In other countries.
The lack of controls on automobile emissions in Western Europe has contributed to extensive damage to forests there. Countries in Eastern Europe have lacked pollution controls altogether and, as a result, have suffered enormous environmental damage.
